In the wall-cases on the west side of this gallery is exhibited a stratigraphical collection, showing a series of rock-specimens, often with their included fossil remains, representing the various geological formations of the British Isles; they are arranged in the order of their sequence in time, commencing near the entrance door with the most recent, and gradually passing down to the most ancient fossil-bearing strata. Along the top of the case is displayed a running section of all the water-formed rocks of England in the order of their succession, each bed being distinctively coloured, and named to correspond with the actual specimens placed beneath. The stratigraphical collection is followed by some illustrations of rock-formation, and certain curious rock-structures simulating fossils. On the east side are exhibited additional specimens of marine Reptiles from the Lias and a series of footprints of Reptiles from the Trias of N. America, the New Red Sandstone of England, etc. FIRST FLOOR. [Sidenote: Gallery of Minerals.] The gallery on this floor, entered from the south end of the east corridor of the hall, contains the extensive Mineral collections, a fuller description of which will be found in special guides.[21] [Sidenote: Introductory Collections.] Entering the gallery the visitor will find, in the first window-case on the left-hand side, a series of specimens selected and labelled to serve as an introduction to the study of Minerals. Beginning with a definition of what is meant by a Mineral, it shows how essential characters were gradually recognised, and how Minerals are distributed into kinds and classified. In the next three window-cases specimens are arranged to illustrate the characters of Minerals and the various terms used in their description. [Sidenote: Rocks.] In the remaining six window-cases on the same side of the gallery, a corresponding series of specimens illustrative of the characters and classification of Rocks is exhibited; and the eleven window-cases on the opposite side contain a collection illustrating the various kinds of Rocks.[22] [Sidenote: General Collection of Minerals.] In the table-cases of the gallery are exhibited specimens of every important Mineral species and variety preserved in the Museum. The cases containing this general collection are numbered from 1 to 41, and the eight panes of each case are severally distinguished by the letters _a_ to _h_. For the use of the student there is published an Index to the names of all the numerous Mineral species and varieties represented in the collection, with references to the table-cases in which the specimens are placed.[23]